Idiopathic Megaesophagus in the Dog: Reasons for Spontaneous Improvement and a Possible Method of Medical Therapy N
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IDIOPATHIC MEGAESOPHAGUS IN THE DOG: REASONS FOR SPONTANEOUS IMPROVEMENT AND A POSSIBLE METHOD OF MEDICAL THERAPY N. Diamant, M. Szczepanski, and H. Mui* INTRODUCTION mine whether similar less-pronounced motor changes could be observed in apparently "nor- DESCRIPTIONS OF IDIOPATHIC MEGAESOPHAGUS mal" dogs, and to determine whether there is a in the dog reveal a variable clinical picture. reasonable basis for using a cholinomimetic drug Reports of either presence or absence of achal- medical therapy. asia are both common, severity of the disorder as a possible method of is inconsistent and improvement in the condi- tion may be described. Although the disorder MATERIALS AND METHODS frequently appears in particular breeds or in Five dogs with idiopathic megaesophagus related animals, sporadic cases are also reported. were studied for periods from two weeks to 24 No specific medical therapy is available and months. (see Figures 2 and 3). The diagnosis surgical disruption of the lower esophageal was made from the clinical signs of persistent sphincter has met with incomplete success (3, regurgitation of swallowed food along with 4, 8, 11-13). radiological demonstration of megaesophagus Sokolovsky has demonstrated again that spon- in the absence of gastroesophageal reflux or vas- taneous improvement can occur with time if the cular compression of the esophagus. There was dogs are fed in an upright position ( 13). He one male German Shepherd (Dog K), two also suggested from radiological studies that miniature Schnauzer litter-mates, one male achalasia is probably not a feature of the condi- (Dog S) and one female (Dog B), and one tion, and that the lower esophageal sphincter female Wire-Haired Fox Terrier (Dog P). The may function normally. More recently, mano- fifth affected animal was a male miniature metric studies have shown that the lower por- Schnauzer (Dog A) born along with two normal tion of the esophageal body has the capacity for mates and resulting from a brother-sister mating peristaltic motor activity and that the lower of the two original minature Schnauzers. esophageal sphincter is in fact functionally nor- Three "normal" dogs were also studied. All mal in dogs with idiopathic megaesophagus (5). were free of regurgitation of swallowed foods, Furthermore, these studies indicated that at and X-ray studies demonstrated clearing of the least two abnormalities contribute prominently esophagus with peristaltic contractions and ab- to the clinical picture seen: (a) a variable por- sence of megaesophagus, hiatus hernia or gastro- tion of middle and upper esophagus lacks con- esophageal reflux. Two female German Shep- tractile activity, and (b) swallowing frequently herd litter mates (Dogs D and L) unrelated to fails to produce motor activity within the func- the achalasia dogs, were studied from the age tional portion of the esophageal body and of three weeks and until the animals were eight sphincter. The severity of these abnormalities months of age. One male minature Schnauzer varies considerably from animal to animal and (Dog X), a litter-mate of the sixth achalasia the abnormalities may improve with time. dog was studied from the age of two weeks to Another feature of interest was also described. 11 months. Although the esophagus in dogs with mega- The dogs were maintained on a standard esophagus did not show hypersensitivity to ration of dry dog chow and water ad lib, and methacholine chloride, administration of this were trained to swallow conventional mano- drug allowed motor activity to appear after a metric recording tubes. After a 12 to 15 hour swallow in the previously nonfunctioning por- fast, the animals were positioned unrestrained tion of the esophagus. on the left side for study. Belt pneumographs The present study was performed to outline around the chest and neck monitored respira- the spontaneous improvement in motor abnor- tion and swallowing respectively and swallow- mality in dogs with megaesophagus, to deter- ing was induced by injecting a bolus of 2-5 ml 'Division of Clinical Science, Department of of water into the pharynx through a separate Medicine of the University of Toronto and Depart- tube. Manometric studies were performed with ment of Gastroenterology, Toronto Western Hospi- multilumen polyvinyl catheter assemblies with tal, Toronto, Ontario. side openings. The tubes were continuously per- f6 CAN. VET. JOUR., vol. 15, no. 3, March, 1974 IDIOPATHIC MEGAESOPHAGUS fused with distilled water by a syringe pump at rates between 0.6 and 2.4 ml/min. At these perfusion rates, pressures to 55 mm Hg can be accurately recorded within 0.5 sec. Pressures < were transmitted to external pressure trans- 100- x.-x ducers' and results graphed on a linear direct- 0 writing ink recorder. Pressures in millimeters of .00 es mercury were read as the mean between inspira- E 80- tory and expiratory deflections. The amplitude L of an esophageal contraction was calculated as 0 - Lw/ the difference between mean resting esophageal pressure and the peak pressure of the contrac- I 60- tion. Each point on the graphs represents the 3: mean of the amplitudes of at least four con- I- 40- tractions. The mean contraction amplitudes of 3: the abnormal dogs were compared to those of the "normal" controls and the T test used to 04-0 r: 20- determine the statistical significance between cn the means. The length of functioning esophagus was determined by withdrawing the recording system through the length of the esophagus with swallowing records obtained at each 1.0 NORMAL DOGS ABNORMAL DOGS cm interval. Motor activity of the esophagus was <6 mo. >6 mo. <6mo. >6mo. also observed by cine X-ray studies after instil- FIGURE 1. Percent response of esophageal body lation of barium into the esophagus through a to swallowing in control and megaesophagus dogs. tube. o - symptomatic dogs with megaesophagus on For determination of the effect of a cholino- X-ray. o - asymptomatic dogs with normal X-ray. mimetic drug on esophageal body motor acti- Each dog is identified by a letter. vity, four pressure recording tips were posi- tioned to span the body of the esophagus. After the esophageal body motor response to swallow- a ten to 15 minute control period urecholine was ing can improve with age and this is noted both given subcutaneously in a dose of 0.1 mgm/kg in dogs with megaesophagus and in apparently and esophageal body activity was then moni- asymptomatic "normal" dogs. Therefore the tored for a subsequent 15 to 20 minutes. The presence or absence of clinical signs and X-ray procedure was repeated on a second day sub- findings of megaesophagus related grossly to stituting a saline injection in place of the ure- the swallowing response. However, Dog K who choline. For each minute, values from two to maintained a poor response to swallowing of six swallows were averaged. 21% became completely asymptomatic with X-ray absence of megaesophagus after six REsULTrs months of age. In this animal, it seemed likely that other factors such as amplitude of the con- Figure 1 outlines the frequency with which traction wave and the length of the nonfunc- esophageal body motor activity occurs follow- tioning segment of esophagus also contributed ing a swallow. A number of points are evident. to the clinical picture of megaesophagus. First, at less than six months of age "normal" The amplitudes of the pressure peaks pro- dogs (D and L) may show a low response to duced by esophageal contractions in the lower swallowing approaching 60%. However, after 5 cm of the esophageal body are graphed for six months of age the "normal" asymptomatic each dog in Figure 2. Again, a number of fea- dogs all had swallowing responses greater than tures are apparent. First, "normal" dogs tended 80%. Second, symptomatic dogs with mega- to have greater contraction pressures than ab- esophagus all had swallowing responses less normal dogs. Second, except for Dog K, the than 60% whether younger or older than six amplitude of the contraction waves was remark- months of age (Dogs A, K, P and B). When ably constant for each dog, including the Dogs S and A with megaesophagus became "normals", over periods as long as 18 to 21 asymptomatic, their swallowing responses in- months. Dog K, initially severely symptomatic creased to greater than 60%. Third, frequency of with marked megaesophagus on X-ray showed a continuous increase in contraction amplitude 'Sanborn 267A, Hewlett-Packard Co., Waltham, over the period of study and this increase paral- Massachusetts. leled his clinical improvement. Prior to nine 67 CANADIAN VETERINARY JOURNAL NORMAL DOGS Normol Dog -6 AFTER WRECHOUNE I 0-a- CONTROL E DOG D 40- E 8 48- I 30- Den. E X 40- E 9 W 20- Q 32- 0 s i 0- -1 A <n 16- z 0 Z 0 8- 0 ABNORMAL DOGS Z 0 30- 0 2 4 6 8 10 12 14 16 16 20 s -J TIME (min.) p ..-a- . uW 20- _ (0 A BO- FIGURE 4. Lower esophageal contraction ampli- 4 Q. tude, after control saline injection and after ure- 0 KA--d ' 11) l0- choline 0.1 mgm/kg in a normal control dog. 40- 3 6 9 12 5 18 21 36- DOG P DOG A AGE (months) 32- Io 26- FIGURE 2. Esophageal contraction amplitude in E 24- control and megaesophagus dogs. Each dog is E 20- 0, .' A identified by a letter. 8 16- I.- i 12- 0. NORMAL DOGS 2 8- 4 60- z 0I- IL)< 40- o 40- - 36- DOG B DOG<S z L*- o 32- ° 20- DID--- _j 28- 4U'> 24- In P., I 20- *^ ., V.-a V C3 a. dI b'sA o 16- U 12- w 80- 8- - AFTER URECHOLINE '-- CONTROL z E1=- 60- U 4 8 12 16 4 12 16 z TIME (min) z 40- 0 FIGURE Lower contraction z 5.